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FROM OROHIPPUS TO MIOHIPPUS

has a well -marked coracoid process. The radius and ulna ar
separate ; so too are the tibia and fibula. MoJiippus, belonging
to the same sub-family, is slightly more primitive ; for the hind
feet have a rudiment of digit I. Orohippus is a little nearer t<
the Horses in that the molar teeth have acquired a little furthe
advance towards the equine type. Instead of the tubercles of th<
teeth remaining for the most part separate, they have fused into s
set of ridges, of which, however, the pattern is less complex thai
in the modern Horses. In other respects Orohippus is much lik<
ffyracotherium. PacJiynolopJius seems to "be "but a synonym.
The next stage is shown by MesoMppus, a JLower Miocene
form, usually referred to the neighbourhood of Pcdaeotheriwrn,. I:
has nearly lost one of the toes of the fore-foot, a rudiment onl]
remaining ; the metapodiais, at any rate of the fore-feet, seem t<
be slightly increased in length. The orbit is not encircled bj
bone, but there is a strong process from the frontal, which nearly
meets the xygoniatic arch.
Anchitherium, from the Upper Miocene, is not far removed ii
structure from the last-mentioned form; it is a trifle nearer th€
existing Horse in several points. The ulna is further reduced anc
fused with the radius below ; the rudiment of digit V is still
more rudimentary ; the two lateral digits are smaller in proportior
to the central one than they are in Mesohippus ; the fibula if
fused below with the tibia. Erom this form to J£qwu& is a small
series of steps, characterised by the still further reduction of all the
digits except III, by the still further reduction of the already
rudimentary ulna and fibula, and by the increasing depth of the
molar teeth, which are of course, in J&gwus, hypselodont.
Another interesting conclusion may seem to follow when we con-
sider the geographical range of the ancestral Horses. Syraaotlierium
and Pa£Jiynolop"hus occurred both in the Old and New World.
I"roai them may have arisen the Horses of both hemispheres.
After that point there is a division, Mesolkippus is American,
and we get at JSquus in that continent through Desma^ippus an<3
Protohi^pus. On the other hand there are no remains known oi
MemMppus in Europe ; and unless subsequent researches prove
the existence of MesoMppus, we have to rely upon forms which
are placed with Anehitherium and JUpparion*
It seems that In America the next genus in the direct line
descent to Memk^ppus is MioMppu®,     It is smaller in